JP2001268391A - Luminance gradation correcting device for video signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminance gradation correcting device capable of suitably operating the gradation correction of a luminance level according to the size of the actual image part of an image. SOLUTION: This device is provided with a masking means for allowing only the luminance signals of pixels within a vertical prescribed detection range of a picture indicated by input luminance signals to pass through a histogram memory for generating and storing the frequency data of each luminance level of the luminance signals outputted from the masking means for each prescribed term, a means for correcting the luminance levels of the input luminance signals, based on the frequency data of the histogram memory, and a detection range setting means for calculating the cumulative value of the frequency data of the luminance signals whose luminance levels are ranging from a zero level to a non-picture display color level among the input luminance signals and setting the prescribed detection range, based on the cumulative value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a luminance gradation correcting device for correcting a luminance gradation of a video signal.

[0002]

2. Description of the Related Art In recent years, as display devices have become larger, it has been required to provide a luminance gradation correction device in order to make images appear sharper. The luminance gradation correction device generally corrects the luminance gradation of a video signal so as to expand the luminance distribution to a dynamic range by supplying the video signal to a non-linear amplifier.

FIG. 1 shows a conventional luminance gradation correction device. This brightness gradation correction device includes a histogram memory 1,
It comprises a maximum correction value calculation circuit 2 and a look-up table memory 3. A digitized luminance signal is supplied to the histogram memory 1 and the look-up table memory 3 as input signals. The histogram memory 1 is a memory for obtaining a luminance distribution of an input luminance signal, and has a storage area addressed by each predetermined plurality of luminance levels, and a frequency is stored in each storage area. Is done. That is, every time a luminance signal for one pixel is supplied, the frequency of the storage area of the histogram memory 1 corresponding to the luminance level increases by one. Further, the stored contents of the histogram memory 1 are all cleared to 0 every predetermined period (one vertical scanning period or an integral multiple thereof), and a new luminance distribution is obtained.

The maximum correction value calculating circuit 2 includes a histogram accumulating circuit 2a for sequentially accumulating data in the histogram memory 1 from low luminance, a cumulative histogram memory 2b for storing the result of the accumulating circuit 2a, and a cumulative histogram memory 2b. A normalization operation circuit 2c for normalizing each data based on the stored data so that the maximum cumulative frequency becomes the maximum value of the output luminance signal. Cumulative histogram memory 2
b, like the histogram memory 1, has a storage area for each of a plurality of luminance levels of the luminance signal, the frequency of which is specified by the luminance level.

The look-up table memory 3 stores the cumulative hiss
Stores data obtained by normalizing the data stored in the program memory
I do. Input the address of the lookup table memory 3
It is specified by the luminance level of the luminance signal, and the specified
The brightness level stored in the dress storage area is normalized.
Is output as a level. FIG. 2 shows such a conventional luminance floor.
The waveform of the brightness conversion operation by the tone correction device is shown.
You. For each pixel of the input luminance signal, the histogram memory 1
Any one of the addresses is specified, and
The value of the storage area is incremented by one. Enter for a predetermined period
The frequency with respect to the luminance level of the power luminance signal is shown in FIG.
Is detected as follows. Here, for simplicity
Brightness level Y₁₅₀, Y₁₆₀, Y₁₇₀, Y_{1 80}, Y₁₉₀, Y
₂₀₀, Y₂₁₀Frequency in the histogram memory 1
Suppose that it was issued. Y₁₅₀<Y₁₆₀<Y₁₇₀<Y₁₈₀<Y₁₉₀
<Y₂₀₀<Y₂₁₀There is a relationship. Frequency within a predetermined period is luminance
Level Y₁₅₀, Y₁₆₀, Y₁₇₀, Y₁₈₀, Y₁₉₀, Y₂₀₀, Y
_{twenty one 0}1,3,5,7,5,3,1
Then, the cumulative frequency becomes the luminance level Y₁₅₀, Y₁₆₀, Y₁₇₀, Y
₁₈₀, Y₁₉₀, Y₂₀₀, Y₂₁₀For 1,4,9,16,
21, 24, 25. That is, as shown in FIG.
As the brightness level increases, the cumulative frequency increases.
It becomes. The maximum value of this cumulative frequency is the maximum output luminance level.
The normalization coefficient is calculated by the normalization operation circuit 2c so that the value becomes a value.
This normalization coefficient is stored in each data of the histogram memory 1.
Data and the result of the multiplication is
It is stored in the storage area of the table memory 3. Look up
Input luminance level and output luminance level of the table memory 3
Is as shown in FIG. 2 (c), and the input luminance signal is
Gradation through look-up table memory 3
The corrected luminance signal is output.

[0006]

However, in such a conventional luminance gradation correcting apparatus, an image represented by an input video signal includes an image of a cinesco size or the like in which a real image portion is narrow in a vertical direction. Fig. 3
As shown by hatching in FIG. 3, there are upper and lower non-image portions (black bands). Therefore, if the detection area of the cumulative histogram is the area surrounded by the dotted line A in FIG. The characteristics are as shown in FIG. That is,
In the cumulative histogram, the frequency of the black level in the non-image portion greatly affects the frequency of the luminance level in the real image portion. There is a problem that adverse effects such as floating occur.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a luminance gradation correction device capable of appropriately performing luminance level gradation correction according to the size of an actual image portion of an image.

[0008]

SUMMARY OF THE INVENTION A luminance gradation correcting apparatus according to the present invention comprises a masking means for passing only luminance signals of pixels within a predetermined detection range in a vertical direction in an image indicated by an input luminance signal, and a masking means. A histogram memory for generating and storing frequency data of each of the luminance levels of the luminance signal output from the CPU at predetermined intervals, a means for correcting the luminance level of the input luminance signal based on the frequency data of the histogram memory, Detection range setting means for obtaining a cumulative value of frequency data for a luminance signal whose luminance level is between zero level and a no-image display color level, and setting a predetermined detection range based on the cumulative value. It is characterized by having.

According to the luminance gradation correcting device of the present invention, the predetermined detection range in the vertical direction of the image indicated by the input luminance signal is set according to the size of the real image portion of the image. In addition, the gradation correction of the luminance level of the input luminance signal can be appropriately performed without being affected by the luminance level of the non-image portion.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 shows a luminance gradation correction device according to the present invention. This luminance gradation correction device is shown in FIG.
As shown in FIG. 1, the A / D converter 11, the sync separation circuit 12, the detection range generation circuit 13 and the masking circuit 14 have the conventional configuration shown in FIG. 1 (histogram memory 1, maximum correction value calculation circuit 2, look-up table memory). It is provided in addition to 3). The A / D converter 11 converts an input video signal (composite signal) into a digital signal. The synchronization separation circuit 12 extracts a vertical synchronization signal and a horizontal synchronization signal of the input video signal, and detects the detection range generation circuit 13 and the masking circuit 1.
4

The detection range generation circuit 13 detects the image size of the input video signal according to the contents of the cumulative histogram memory 2b in the maximum correction value calculation circuit 2 and sets the detection range of the video signal. The masking circuit 14 is connected to the output of each of the A / D converter 11 and the detection range generation circuit 13, and supplies a digital video signal in the detection range set by the detection range generation circuit 13 to the histogram memory 1.

Since the histogram memory 1, the maximum correction value calculation circuit 2 and the look-up table memory 3 are the same as those shown in FIG. 1, further explanation is omitted here. Although not shown, when the input video signal is a color video signal, for example, a YC separation circuit is provided after the A / D converter 11 and the separated luminance signal is supplied to the masking circuit 14. Is performed.

Here, it is assumed that the size of the real image portion of the input video signal includes a 4: 3 image, a Vista size, and a cinesco size. When the input video signal is a 4: 3 image, the actual image is formed by 199 lines from the 39th scanning line to the 237th scanning line. When the input video signal is a Vista size image, the actual image is formed by 167 lines from the 56th line to the 222nd line of the scanning line.
When the input video signal is an image of a cinesco size, the actual image is formed of 139 lines from the 70th line to the 208th line.

In this embodiment, a 4: 3 size image and a Vista size image are used as a detection range of a real size portion of a Vista size image, and a Cinesco size image portion is detected as a real image portion. Range. Next, the operation of the detection range generation circuit 13 will be described with reference to the flowchart of FIG. When the result of the accumulation circuit 2a is stored in the accumulation histogram memory 2b for each field of the input video signal, the detection range generation circuit 13 changes the luminance level from a zero level to a black band display level (non-image display color level). The accumulated value Acm (b) of the frequency data is detected (step S
1). That is, the histogram accumulation circuit 2a calculates the cumulative frequency at which the number of appearances is accumulated in the range of the luminance level of the video signal in the range of 0 to 255 for each field, and stores it in the cumulative histogram memory 2b. Therefore, the cumulative frequency of the black band display level in the cumulative frequency of the luminance levels 0 to 255 is obtained as the cumulative value Acm (b).

The detection range generation circuit 13 calculates the accumulated value Acm (b)
Is greater than or equal to the threshold value Thrd (step S2). If Acm (b)> Thrd, the detection range is
(X is an integer equal to or more than 1) lines (step S3). In this step S3, calculation is performed to increase the number of vertical delay lines Vdlyline by x and decrease the number of vertical detection range lines Vdetline by 2x. After the execution of step S3, the detection range generation circuit 13 determines whether or not the number of vertical detection range lines Vdetline as a result of the calculation is smaller than the reference line number Cinline of the Sinesco-sized image (step S4). When Vdetline <Cinline, the detection range is narrower than that of the cinesco-size image. Therefore, the number of vertical delay lines Vdlyline is made equal to the reference delay line number Cindly of the cinesco-size image, and the number of vertical detection lines Vdetline is set to the reference line. Number Cinline
(Step S5). Vdetline ≧ Cinlin
In the case of e, the number of vertical delay lines Vdlyline and the number of vertical detection range lines Vdetline calculated in step S3 are maintained as numerical values of a new detection range.

If Acm (b) .ltoreq.Thrd in step S2, the detection range is increased by upper and lower y (y is an integer of 1 or more) lines (step S6). In step S6, calculation is performed to decrease the number Vdlyline of vertical delay lines by y and increase the number Vdetline of vertical detection range by 2y. After executing step S6, the detection range generation circuit 13 sets the vertical detection range line number Vdetline of the calculation result to the reference line number Visline of the Vista size image.
It is determined whether it is larger (step S7). Vde
If tline> Visline, the detection range is wider than the Vista size, so the number of vertical delay lines Vdlylin
e is made equal to the reference delay line number Visdly of the Vista size image, and the vertical detection range line number Vdetline is made equal to the reference line number Visline (step S8). Vdetlin
If e ≦ Visline, the number of vertical delay lines Vdlyline and the number of vertical detection range lines Vd calculated in step S6
etline is maintained as a new detection range value.

The detection range generation circuit 13 supplies the number of vertical delay lines Vdlyline and the number of vertical detection range lines Vdetline set as described above to the masking circuit 14 as detection range data (step S9). Masking circuit 14
The digital video signal supplied from the A / D converter 11 is converted into a vertical detection range line after a lapse of a horizontal scanning period of the number of vertical delay lines Vdlyline set in the detection range generating circuit 13 in response to the vertical synchronization signal. The data is output to the histogram memory 1 over a horizontal scanning period of several Vdetlines.

FIG. 7 shows a period corresponding to each of the number of vertical delay lines Vdlyline and the number of vertical detection range lines Vdetline in one feed of the input video signal. This FIG.
In the period, the video signal is not supplied from the masking circuit 14 to the histogram memory 1 during the period corresponding to the vertical delay line number Vdlyline, and the video signal is supplied from the masking circuit 14 to the histogram memory 1 during the period corresponding to the vertical detection range line number Vdetline. You.

When the input video signal is a 4: 3 image,
The detection range for the image becomes the Vista size (portion surrounded by a broken line) as shown in FIG. 8A, and the cumulative histogram for each luminance level of the video signal of the 4: 3 image is as shown in FIG. 9A. Characteristics. The cumulative value Acm (b) of the cumulative histogram in FIG. 9A is equal to or smaller than the threshold value Thrd. It is assumed that the input video signal has changed from a 4: 3 image to a Cinesco size image as shown in FIG. The hatched portion in FIG. 8B is a black band attached to the cinesco-sized image. The cumulative histogram in the field at this time has the characteristic as shown in FIG. 9B, and the cumulative value Acm (b) of the frequency data when the luminance level is between the zero level and the black band display level increases. Since the accumulated value Acm (b) is larger than the threshold value Thrd, the detection range is narrowed by x lines (for example, two lines) above and below the image as indicated by broken lines in FIG. 8C. As a result, the accumulated value Acm (b) decreases as shown in FIG.

In the following fields, Acm (b)> Thrd
As long as the detection range is repeatedly set to be narrower by x lines above and below the image, the detection range for the image is gradually narrowed, and the cumulative value Acm (b) of the cumulative histogram is gradually reduced. I do. As a result, the detection range becomes the Sinesco size as shown in FIG. 8D by performing the above steps S4 and S5, and the cumulative histogram for each luminance level of the video signal of the Sinesco size image is shown in FIG. 9D. The characteristics are as follows.

In the luminance gradation correcting apparatus according to the present invention, since the luminance data of the real image portion of the image of one field is supplied to the histogram memory 1, the luminance level formed in the histogram memory 1 is obtained. The data table showing the frequency data for each pixel does not include the frequency of the luminance at the black band display level. Therefore, the cumulative histogram data table is formed in the cumulative histogram memory 2b without accumulating the luminance frequency of the black band display level. Since the look-up table memory 3 stores data obtained by normalizing the data stored in the cumulative histogram memory 2b, it is possible to eliminate the influence of the luminance of the black band portion on the gradation correction of the luminance data. In other words, even in the case of an image of a cinesco size or the like having black bands above and below the display image, gradation correction can be performed without black floating in the actual image portion. Further, a complicated circuit is not required for detecting video signals having different sizes of real image portions such as a cinesco size, a Vista size, and the like, and the vertical size of the detection range is increased or decreased for each field. Since it is performed gradually, there is no sudden change in image quality.

In the above-described embodiment (flow chart of FIG. 6), the predetermined detection range is increased and decreased by the same number of lines on the upper and lower sides. May be different from each other.
In the above-described embodiment, the cumulative value Acm (b) is compared with a single threshold Thrd to determine whether the detection range is increased or decreased. However, two thresholds, Thrd-d and Thrd-u, are used. May be. Thrd-d> Thrd-u, and the threshold value Thrd-d and the threshold value Thrd
The difference from -u is made larger than the change of the accumulated value Acm (b) due to the number of increase / decrease lines 2y, 2x for each field. For example, if x = y = 2, Thrd-d = Thrd-u + 5
It is. When two thresholds Thrd-d and Thrd-u are used, as shown in FIG. 10, after execution of step S1, first, whether or not the accumulated value Acm (b) is larger than the threshold Thrd-d is determined. Is determined (step S2a). If Acm (b)> Thrd-d, the process proceeds to step S3. On the other hand, if Acm (b) ≦ Thrd-d, it is determined whether or not the accumulated value Acm (b) is smaller than the threshold value Thrd-u (step S2b). If Acm (b) <Thrd-u, the process proceeds to step S6. Thrd-d ≧ Acm (b) ≧ Thrd-u
Then, the detection range data (vertical delay line number Vdlyline and vertical detection range line number Vdet) set in the previous field
line) is supplied to the masking circuit 14 (step S
9). By such an operation, the number of vertical detection range lines Vdetline is decreased in one field because the determination result of step S2 is Acm (b)> Thrd. In the next field, the determination result of step S2 is Acm (b). ) ≤ Thrd
As a result, there is no need to repeatedly increase or decrease the Vdetline for each field, such as increasing the number Vdetline of the vertical detection range lines, and more stable luminance gradation correction can be performed.

Further, in the above embodiment, the number of increase / decrease lines 2y and 2x for each field is a fixed value.
The number of increase / decrease lines is 2 according to the difference between the current vertical detection range line number Vdetline and the reference line number Cinline of the Sinesco size image or the reference line number Visline of the Vista size image.
y and 2x may be changed. For example, when the difference between the current vertical detection range line number Vdetline and the reference line number is equal to or greater than a predetermined value, the number of increase / decrease lines 2y, 2x is increased, and when the difference is smaller than the predetermined value, the increase / decrease line number 2y, 2x is decreased. Can be.

In the above-described embodiment, the threshold T
Although hrd is set to a constant value, the threshold value Thrd may be changed according to the current vertical detection range line number Vdetline. For example, the threshold value Thrd can be set as in the characteristic shown in FIG. That is, when the detection range (the number of vertical range detection lines) is near the Cinesco size, the threshold value is set to a constant threshold value Thrd so that the detection range does not vibrate, and thereafter, as the number of vertical range detection lines increases, the black band of the Cinesco size image increases. The threshold value Thrd is increased at a gradient smaller than the gradient of the cumulative value of the section. As a result, in the case of the Vista size image, when the detection range is the number of lines of the Vista size image, and there is a signal at or below the black band display level in the image, the margin for starting to reduce the number of lines is improved.

FIG. 12 shows another embodiment of the present invention. In this embodiment, the detection range is 4: 3 image,
It can be adjusted to three sizes, Vista size and Sinesco size. The configuration of the luminance gradation correction device shown in FIG. 12 is different from that of FIG.
Device. The 4: 3 image detection circuit 15 is connected to the output of the A / D converter 11 and detects that the image indicated by the output digital video signal of the A / D converter 11 is a 4: 3 image. In the case of the 4: 3 image, unlike a Cinesco size image and a Vista size image, a predetermined number (for example, 5) lines and a lower end (scanning line 237 lines) from the upper end (the 39th scanning line) of the actual image range Since the luminances of a predetermined number of lines up to the eye) are not all lower than the black band display level, the 4: 3 image detection circuit 15 determines that the luminances of all the lines are not lower than the black band display level. It is determined that there are three images, and if all the luminances of these lines are lower than the black band display level, it is determined that the image is other than the 4: 3 image. 4: 3
A signal indicating the detection result of the image detection circuit 15 is supplied to the detection range generation circuit 13.

Next, the operation of the detection range generation circuit 13 in the case of the apparatus of FIG. 12 will be described with reference to the flowchart of FIG. When the result of the accumulation circuit 2a is stored in the accumulation histogram memory 2b for each field of the input video signal, the detection range generation circuit 13 converts the input video signal to 4: 4 in accordance with the output signal of the 4: 3 image detection circuit 15. It is determined whether or not the signal is a signal of three images (step S11). If the input video signal is a 4: 3 image signal, the detection range is set to the upper and lower z
It is increased by the number of lines (step S12). In step S12, the number of vertical delay lines Vdlyline is reduced by z, and the number of vertical detection range lines Vdetline is reduced by two.
A calculation to increase by z is performed. Detection range generation circuit 1
In step S3, after execution of step S12, it is determined whether or not the vertical detection range line number Vdetline of the calculation result is larger than the reference line number Baseline of the 4: 3 image (step S12).
13). In the case of Vdetline> Baseline, the detection range is wider than the size of the 4: 3 image, so the number of vertical delay lines Vdlyline is made equal to the reference delay line number Basely of the 4: 3 image, and the number of vertical detection range lines is set. Vdetlin
e is made equal to the reference line number Baseline (step S
14). If Vdetline ≦ Baseline, step S
The number of vertical delay lines Vdlyline and the number of vertical detection range lines Vdetline calculated in 12 are kept as they are as the numerical values of the new detection range.

The detection range generating circuit 13 supplies the vertical delay line number Vdlyline and the vertical detection range line number Vdetline set as described above to the masking circuit 14 as detection range data (step S9). Detection range generation circuit 1
If the input video signal is determined to be a signal other than the 4: 3 image in step S11, it is determined whether the current vertical detection range line number Vdetline is larger than the reference line number Visline of the Vista size image. Is determined (step S15). If Vdetline> Visline, the detection range is reduced by upper and lower a (a is an integer of 1 or more) lines (step S16). In this step S16,
A calculation is performed in which the number of vertical delay lines Vdlyline is increased by a and the number of vertical detection range lines Vdetline is reduced by 2a. After executing step S16, the detection range generation circuit 13 proceeds to step S9.

The detection range generation circuit 13 determines in step S15
If it is determined that Vdetline ≦ Visline in FIG.
The detection range data corresponding to the Vista size image or the Sinesco size image is generated by performing the operations of steps S1 to S9 shown in FIG. When the input video signal is a 4: 3 image,
The detection range for the image is a range indicated by a dashed line in FIG. 14A, and the vertical detection range number of lines Vdetlin of the 4: 3 image
e is the reference line number Baseline.

FIG. 14 shows an example in which the input video signal is 4: 3.
It is assumed that the image has changed to a Vista size image as shown in FIG. At this time, the luminance of the predetermined number of lines from the 39th scanning line to the predetermined number of lines and the 237th scanning line in the field is all below the black band display level.
The operations of steps S15 and S16 are repeated to
As shown in (c), the image detection range, that is, the vertical detection range line number Vdetline is gradually reduced. Step S
When it is determined in step 15 that Vdetline ≦ Visline, the detection range finally becomes the range of the Vista size indicated by the dashed line as shown in FIG. 14D through the operations of steps S1 to S8, and the number of vertical detection range lines Vdetline is Reference line number Vi
It becomes sline.

In the above-described embodiment, the non-image display color level, which is the luminance level of the non-image portion of the image, is described as the black band display level. However, the non-image portion is not limited to black. Of course, the color level may be the luminance level of another display color.

[0031]

As described above, according to the present invention, the predetermined detection range in the vertical direction of the image indicated by the input luminance signal is set according to the size of the real image portion of the image. The gradation correction of the luminance level of the input luminance signal can be appropriately performed without being affected by the luminance level of the non-image portion.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a conventional luminance gradation correction device.

FIG. 2 is a characteristic diagram for explaining an operation example of the device of FIG. 1;

FIG. 3 is a diagram illustrating a display example of an image in which an actual image portion is narrow in a vertical direction.

FIG. 4 is a diagram showing a cumulative histogram of luminance levels of the image of FIG. 3;

FIG. 5 is a block diagram showing an embodiment of the present invention.

FIG. 6 is a flowchart showing an operation of a detection range generation circuit in the apparatus of FIG.

FIG. 7 is a diagram illustrating a vertical delay line number Vdlyline and a vertical detection range line number Vdetline.

8 is a diagram showing changes in the number of vertical delay lines Vdlyline and the number of vertical detection range lines Vdetline when changing from a 4: 3 image to an image of a cinesco size in the apparatus of FIG. 5;

FIG. 9 is a diagram illustrating a cumulative histogram in the case of a change in the detection range in FIG. 8;

FIG. 10 is a flowchart illustrating another operation of the detection range generation circuit.

FIG. 11 is a diagram illustrating a threshold Thrd setting characteristic corresponding to a vertical detection range line number Vdetline.

FIG. 12 is a block diagram showing another embodiment of the present invention.

FIG. 13 is a flowchart showing the operation of a detection range generation circuit in the device of FIG.

14 is a diagram showing changes in the number of vertical delay lines Vdlyline and the number of vertical detection range lines Vdetline when changing from a 4: 3 image to a Vista size image in the apparatus of FIG. 12;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Histogram memory 2 Maximum correction value calculation circuit 3 Look-up table memory 12 Synchronization separation circuit 13 Detection range generation circuit 14 Masking circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroshi Honda 2680, Nishihana, Tatomi-cho, Nakakoma-gun, Yamanashi Prefecture Pioneer Corporation F-term (reference) 5C021 PA53 PA56 PA58 PA63 PA67 PA77 PA80 PA85 SA02 SA03 XA35 5C082 AA02 BA20 BA34 BA35 BA41 BB49 BD01 BD02 CA11 CA18 CA81 CA84 CB01 DA71 DA76 DA87 MM02 MM08

Claims (9)

[Claims] 1. A masking means for passing only a luminance signal of a pixel within a predetermined detection range in a vertical direction in an image indicated by an input luminance signal, and frequency data of each luminance level of the luminance signal output from said masking means A histogram memory that creates and stores the data for each predetermined period, a unit that corrects the luminance level of the input luminance signal based on the frequency data of the histogram memory, and a luminance level of the input luminance signal from a zero level. Detection range setting means for obtaining a cumulative value of the frequency data for a luminance signal up to the non-image display color level, and setting the predetermined detection range based on the cumulative value. Tone correction device. 2. The detection range setting means compares the cumulative value with a predetermined threshold value, and when the cumulative value is larger than the predetermined threshold value, sets a first predetermined number of lines above the predetermined detection range. And changing to a range reduced by a second predetermined number of lines on the lower side, and when the accumulated value is smaller than the predetermined threshold, the predetermined detection range is set on the upper side by a third predetermined number of lines and on the lower side. 2. The luminance gradation correcting device according to claim 1, wherein the range is changed to a range in which the number is increased by a fourth predetermined number of lines. 3. The histogram memory according to claim 1, wherein the frequency data is created and stored for each field period, and the detection range setting means sets the predetermined detection range for each field period. The brightness gradation correction device according to claim 1. 4. A first threshold and a second threshold are provided as the predetermined threshold, and a difference between the first threshold and the second threshold is set to 1
3. The luminance gradation correction device according to claim 2, wherein a change in the accumulated value due to a change in the predetermined detection range per field period is set larger. 5. The luminance gradation correction apparatus according to claim 1, wherein a change amount of the predetermined detection range per one field period is set according to an actual image size of an image indicated by the input luminance signal. . 6. When the difference between the predetermined detection range and the actual image size of the image indicated by the input luminance signal is larger than a predetermined value,
When the difference between the predetermined detection range and the actual image size of the image represented by the input luminance signal is smaller than the predetermined value, the change in the predetermined detection range per field period is smaller than the predetermined value. 6. The brightness gradation correction device according to claim 5, wherein a change in the range is small. 7. The luminance gradation correction device according to claim 2, wherein the predetermined threshold is changed according to an actual image size of an image indicated by the input luminance signal. 8. The luminance gradation correcting device according to claim 2, wherein the predetermined threshold value is increased as the actual image size of the image indicated by the input luminance signal increases. 9. The detection range setting means determines whether an image indicated by the input luminance signal is a 4: 3 image, and if the image is a 4: 3 image, sets the predetermined detection range to 4: 3.
If it is not a 4: 3 image, it is determined whether the current predetermined detection range is larger than the actual image range of the Vista size image, and the current predetermined detection range is determined. Is smaller than the real image range of the Vista size image, the predetermined detection range is reduced for each of the predetermined periods, and if the current predetermined detection range is less than or equal to the real image range of the Vista size image, 2. The luminance gradation correction device according to claim 1, wherein the predetermined detection range is set based on an accumulated value.